My logic is right but test cases are very hude numbers.... failed to evaluate...
You need to learn to avoid loops. You can use isprime on an array. In any case, your logic is wrong. You never test that b is prime.
As Guillaume pointed out, this solution doesn't test if the numbers in b are Mersenne primes, simply if they're less than 2^n-1, which is not the right criterion. Further, you concatenate the index of the loop (j, which goes from 1 to 1...), rather than a Mersenne prime to b.
Also, this problem is designed, as many of James's problems are, to fail by timeout unless vectorized solutions are used.
i have corrected the logic but plz can u tell me smthing about vectorized solutions...
u can also mail me on firstname.lastname@example.org
some tips: http://nl.mathworks.com/help/matlab/matlab_prog/techniques-for-improving-performance.html
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